People have been increasingly paying attention to recycling of electronic parts in recent years because of environmental concerns. Particularly, recycling of printed circuit boards of electronic products such as personal computers and printers is a very serous problem to be dissolved.
Circuits that need recycling include power supply circuits. Power supply circuits normally contain electrolytic capacitors. Electrolytic capacitors have only a short service life if compared with other electronic parts. In addition, generally in a power supply circuit, electrolytic capacitors are arranged close to parts generating a large amount of heat and therefore, the service life of electrolytic capacitors can be further shortened by such heat. If there is something wrong with an electrolytic capacitor contained in an electronic product, it can seriously affect other electronic parts surrounding it. Therefore, electrolytic capacitors and other electronic parts having only a short service life are manually replaced and the other electronic parts are reutilized by following procedure that includes the steps listed below.    1. Visually confirm the electronic part to be replaced.    2. Remove the solder between the electronic part to be replaced and the printed substrate.    3. Remove the electronic part to be replaced from the printed substrate.    4. A replacement electronic part is inserted into the printed substrate.    5. Solder the replacement electronic part to the printed substrate.    6. Visually confirm the newly soldered replacement electronic part.
Meanwhile, Japanese Patent Application Laid-Open No. 6-61621 describes a technique of functionally separating a plurality of circuit sections on a single printed circuit board so that only the circuit section that has turned out to be defective can be replaced by a corresponding replacement circuit section that is commercially available. Japanese Patent Application Laid-Open No. 6-61621 also describes that detachable partitioning sections are arranged among the separated circuit sections and each of the circuit sections is provided with an interface.
However, the above described known technique of steps 1 through 6 for replacing an electronic part such as an electrolytic capacitor is accompanied by the following problems.                Tremendous time and efforts have to be spent in the steps for replacing an electronic part.        Since the soldering operation necessary for replacing an electronic part generates heat, means for protecting the operator has to be provided.        The heat generated by the soldering operation necessary for replacing an electronic part can peel off, if partly, the circuit pattern and/or reduce the reliability of the circuit pattern.        A wrong electronic part can be used as replacement at the time of replacing an electronic part.        The polarities of the replacement electronic part can be inverted at the time of replacing an electronic part.        
In recent years, small packaged switching power supply units have been frequently used. The switching power supply unit is formed independently from the electronic product in which it is used and hence it is required to be replaced and reused in a simple and reliable way. More specifically, switching power supply units have to be so designed that the user can easily replace the switching power supply unit of his or her own electronic product.
With the technique described in the above cited Japanese Patent Application Laid-Open No. 6-61621, the frame of the electronic product needs to be opened and the printed substrate to be replaced has to be separated from-the printed circuit board in the inside. Subsequently, a replacement printed substrate needs to be connected and the frame has to be closed once again. Thus, the user may not feasibly use such a technique.